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321.
Takeharu Haino 《Tetrahedron letters》2004,45(11):2281-2284
Shape-selective recognition for the dicarboxylates in DMSO can be attained by a new calix[4]arene-based receptor 1 having two urea groups. Biologically active chorismate selectively bound in 1 over its dehydrated derivative. Molecular mechanics calculations gave a plausible explanation for the selective binding. 相似文献
322.
K. A. Lyssenko D. V. Lyubetsky M. Yu. Antipin I. L. Odinets 《Russian Chemical Bulletin》2005,54(11):2484-2491
The nature of the intramolecular O—H...O bond was studied and its energy was estimated by X-ray diffraction analysis and quantum-chemical
calculations (B3LYP/6-311G**) of (diphenylphosphoryl)acylacetonitriles. The influence of the nature of the substituents at
the double bond in the H-bonded ring and the crystal packing effects on the hydrogen bond were investigated.
Dedicated to Corresponding Member of the Russian Academy of Sciences T. A. Mastryukova.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2406–2413, November, 2005. 相似文献
323.
利用吡啶吸附-IR,NH3吸附-脱附,原位热重积炭,DSC等技术并结合甲基环己烷(MCH)脱氢活性试验,研究了K2O对工业Pt-Sn/Al2O3催化剂的表面酸性及MCH脱氢稳定性的影响,结果表明,K2O能有效地调变催化剂的表面酸性,降低其表面酸中心特别是强酸中心的数目;MCH脱氢反应的积炭量随K2O含量的增加而减少,但催化剂的高温脱氢稳定性与K2O含量并不完全呈顺变关系,K2O含量应严格控制,当K 相似文献
324.
Lourdes Callau Ana Mantecn Jos Antonio Reina 《Journal of polymer science. Part A, Polymer chemistry》2002,40(14):2237-2244
We performed the crosslinking of vinyl‐terminated biphenyl and naphthalene side‐chain liquid‐crystalline polyethers using peroxide‐type initiators with and without the addition of tertiary amine promoters. The crosslinking temperatures were chosen in the range of mesophase stability to allow the mesophase order to be frozen. The biphenyl derivatives, with a high isotropization temperature, were crosslinked to a large extent. This led to anisotropic thermosets. To crosslink naphthalene derivatives, amine promoters were needed, but degrees of crosslinking were lower, and anisotropic elastomers were obtained. Crosslinking processes were studied by differential scanning calorimetry, polarized optical microscopy, and Fourier transform infrared spectroscopy. The nature of the frozen mesophase was confirmed by X‐ray diffraction studies on mechanically oriented samples. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2237–2244, 2002 相似文献
325.
H.?Hussain H.?U.?Rehman Z.?AhmadEmail author 《Journal of Sol-Gel Science and Technology》2005,36(3):239-248
Nano-composites from aramid-silica system have been prepared via sol-gel process. Poly (phenyleneterephthalamide) copolymer
chains were prepared by reacting a mixture of p- and m-phenylenediamines with terephthaloyl chloride in dimethylacetamide used as solvent. The sol-gel process in the polymer
matrix was carried out through hydrolysis and condensation of a mixture of tetraethoxysilane and (3-glycidoxypropyl) trimethoxysilane.
The latter was used to develop linkage, on one hand with silica network structure using alkoxy groups and on the other hand
with aramid chains at its secondary amine groups through glycidal groups of silane. Mutual interaction between the two disparate
phases aramid and silica network was thus created. Thin films of the composites containing different proportions of silica
ranging from 5.0 to 25.0-wt% were cast by the solvent elution technique. The α-relaxation temperature associated with the
glass transition was measured by the dynamic mechanical thermal analysis. The results showed an increase in the glass transition
temperature from 328°C for the pure aramid to 352°C for the hybrid materials containing 25-wt% silica, an indicative of the
increased interfacial interaction between the two phases. Films having relatively low silica content were flexible and transparent,
but those with high silica content were opaque and brittle. These films were tested for their tensile strength, modulus and
toughness. The mechanical strength of the composites as compared to the pure aramid increased initially but with further addition
of silica the strength decreased. The initial increase can be explained due to increased interfacial interaction between the
two phases, however agglomeration of silica particles was responsible for decreasing strength at higher silica contents. 相似文献
326.
Odin C 《Magnetic resonance in chemistry : MRC》2004,42(4):381-388
A variable-temperature high-resolution 13C and 87Rb solid-state NMR study of powder rubidium hydrogencarbonate, RbHCO3, is presented for the first time. At ambient temperature, RbHCO3 is formed by centrosymmetric dimers linked by hydrogen bonds, but almost no information is available on this compound concerning proton disorder and the low-temperature phase. However, potassium hydrogencarbonate, KHCO3, which has an isomorphic structure for the high temperature phase, was well studied: it undergoes a non-ferroic, non-ferroelectric phase transition at Tc = 318 K between two monoclinic structures. The protons are disordered in an asymmetric double-well potential in the low-temperature phase, and the double-well potential becomes symmetric in the high-temperature phase. By comparison with recent solid-state NMR experimental results on KHCO3, we show that RbHCO3 undergoes a phase transition at Tc approximately 245 K, and give evidence that the proton dynamic disorder in both compounds is very similar. 相似文献
327.
W. Mikenda F. Pertlik E. Steinwender 《Monatshefte für Chemie / Chemical Monthly》1993,124(8-9):867-875
Summary X-ray structural data are reported for 2-hydroxy-benzhydrazide(monoclinic; P21/n-C
2h
5
;a=10.569(2) Å,b=11.264(2) Å,c=6.074(1) Å, =98.80(1)°;Z=4;R=0.054) and 2-hydroxy-thiobenzhydrazide (monoclinic; P21/n-C
2h
5
;a=14.598(6) Å,b=5.975(2) Å,c=9.286(4) Å, =107.80(3)°;Z=4;R=0.044). In both compounds the phenolic OH groups are intramolecularly hydrogen bonded to the (thio)carbonyl oxygens and sulfurs, respectively; the basic intermolecular association patterns consist of closed six-membered hydrogen bonded dimers which are connected via N-H ... NH2 hydrogen bonds. The spectral characteristics of the intramolecular O-H...O/S hydrogen bonds (solid state
(OH)=2800/2700 cm–1, CCl4 solution
(OH)=3035/3100 cm–1, CDCl3 solution (OH)=11.62/10.56 ppm) are similar to those of corresponding primary and secondary amides. The solid state IR spectra are consistent with hydrogen bonded NH groups and free NH2 groups, the solution IR spectra indicate free NH2 as well as free NH groups.
Wasserstoffbrückenbindung in 2-Hydroxy-benzhydrazid und 2-Hydroxy-thiobenzhydrazid. Strukturelle und spektroskopische Untersuchungen
Zusammenfassung Es werden Röntgenstrukturdaten für 2-Hydroxy-benzhydrazid (monoklin; P21/n- C 2h 5 ;a=10.569(2) Å,b=11.264(2)Å,c=6.074(1)Å, =98.80(1)°;Z=4;R=0.054) und 2-Hydroxy-thiobenzhydrazid (monoklin; P21/n - C 2h 5 ;a=14.598(6)Å,b=5.975(2)Å,c=9.286(4)Å, =107.80(3)°;Z=4;R=0.044) berichtet. In beiden Verbindungen bilden die phenolischen OH-Gruppen intramolekulare Wasserstoffbrücken mit den Carbonyl-Sauerstoff-, bzw. den Thiocarbonyl-Schwefel-Atomen. Das intermolekulare Assoziationsmuster wird durch N-H...NH2 Wasserstoffbrücken bestimmt, die jeweils zwei Moleküle über sechszählige Ringe zu Dimeren verbinden. Die IR- und NMR-spektroskopischen Charakteristika der intramolekularen O-H...O/S Wasserstoffbrücken (kristallin: (OH)=2800/2700 cm–1, CCl4-Lösungen: (OH)=3035/3100 cm–1, CDCl3-Lösungen: (OH)=11.62/10.56 ppm) sind sehr ähnlich zu denen entsprechender primärer und sekundärer Amide. Die Festkörper-IR-Spektren stehen in Einklang mit assoziierten NH- und freien NH2-Gruppen, während die Lösungs-IR-Spektren auch auf das Vorliegen freier NH-Gruppen schließen lassen.相似文献
328.
meso-Tetraphenylporphyrin (and its derivatives), in the reaction with fuming yellow nitric acid (d=1.53), form either 5-(4-nitroaryl)-10,15,20-triarylporphyrin, 5,10-bis(4-nitroaryl)-15,20-diarylporphyrin, or 5,10,15-tris(4-nitroaryl)-20-arylporphyrin, depending on the reaction temperature (0-20 °C), amounts of the acid used, and reaction time. The above nitroporphyrins react, in the presence of a base (t-BuOK) at 0 °C, with carbanions (which bear nucleophugal groups at the carbanionic center: −CH(Cl)SO2Tol, −CH(Br)SO2Tol, and −CH(Cl)SO2NMe2), leading to the nucleophilic substitution of hydrogen in one or more of the meso-nitroaryl rings. By this route, the preparation of the highly substituted ‘synthetic’ porphyrins (bearing up to ten O-, N-, Cl-, or C-substituents) was demonstrated. 相似文献
329.
Grzegorz WojciechowskiMa?gorzata Ratajczak-Sitarz Andrzej KatrusiakBogumil Brzezinski 《Journal of Molecular Structure》2002,612(1):59-64
The crystals of 5,5′-dibromo-3-diethylaminomethyl-2,2′-biphenol N-oxide were studied by X-ray and FT-IR spectroscopy. Within this molecule two short OHO intramolecular hydrogen bonds are formed. The NO?H+?O− bond between the OH and the N-oxide groups is very strong, of 2.419(7) Å between the oxygen atoms. The proton potential of this hydrogen bond is flat, broad and has probably no barrier—consequently it could not be located from X-ray diffraction data. The other hydrogen bond formed between two hydroxyl groups appears asymmetrical from FT-IR spectra, and shows also relatively limited proton polarizability. The molecular conformation is non-planar, due to strong overcrowding effect between the oxygen atoms involved in the hydrogen bonds. 相似文献
330.
The purpose of this research was to select an activated carbon and alkaline solution blend that generated the best H2S adsorption on alkaline-activated carbon. RB2 (activated carbon) impregnated with NaOH solution was shown to have the optimum H2S removal efficiency. The optimum NaOH concentration was 50 mg per gram of carbon. H2S adsorption via RB2-NaOH50 was five times that of a corresponding fresh-activated carbon. The adsorption equivalent of H2S is nearly 1 (mol-H2S/mol-AOH), therefore, H2S + AOH AHS + H2O was the major reaction. The H2S adsorption isotherm corresponded to the Freundlich isotherm. 相似文献